Method and apparatus for spinning high strength silk from cuprammonium cellulose solutions



Dem 1956 v. ELSAESSER 2,773, 81

METHOD AND APPARATUS FOR SPINNING HIGH STRENGTH SILK FROM CUPRAMMONIUM CELLULOSE SOLUTIONS Filed April 7, 195a INVENTOR ATTORNEY METHOD AND APPARATUS FOR SPINNING HIGH STRENGTH SILK FROM CUPRAMMONIUM CEL- LULOSE SOLUTIONS Viktor Elsaesser, Leverkusen, Germany, assignor to J. P. Bemberg Aktiengesellschaft, Wiippertal-Oberbannen, Germany, a joint-stock company of Germany Application April 7, 1953, Serial No. 347,208

2 Claims. (Cl. 18-8) This invention relates to artificial silk manufacture, and more particularly to the manufacture of high strength silk from a cuprammonium cellulose solution.

The textile characteristics of a textile filament, and particularly its strength and elongation are closely interrelated to the arrangement of the molecular or micellar structural elements thereof. With filaments of regenerated cellulose, this arrangement is essentially determined by the spinning method.

I have studied, with particular reference to the cuprammonium stretch-spinning method, the influence of the spinning method on the micelle structure of the filaments, and their relationship to the textile characteristics thereof, with the object of influencing this structure at will by corresponding modifications of the spinning process.

A primary object of this invention is to provide a method of manufacturing from a cuprammonium cellulose solution silk of particularly high strength.

Other objects, and the manner inwhich they are attained, will become apparent as this specification proceeds.

In accordance with the present invention I have discovered that in order to attain a particularly high strength of the filament, three essential conditions must be observed, to wit:

1. The parallel orientation of the micelles brought about in the course of the stretching step must not be affected detrimentally, from the surface, by excessive frictional forces arising between the filament and the precipitating bath.

2. The tensile stress on the capillary filament, required for satisfactory orientation purposes, must attack in a particular region of the state of coagulation, the experimentally determined optimum state defined by a viscosity of the filament mass of from about 50,000 to about 60,000 poise.

3. The stretching (or orientation) procedure must take place, in this region, as slowly as possible.

The first condition noted above renders it necessary to maintain the relative velocity between the filament and the spinning bath, at a very low value.

As to the second condition discussed above, it is noted that the existence of a so-called optimum state and its significance with respect to the ultimate structure of the filament, per se, have been known for some time.

In order to implement the basic concepts of the invention, recourse is had to an empirical formula which permits calculating the point within the funnel where under the prevailing spinning conditions, the filament is in the optimum state.

This point (distance from the spinning nozzle=a) can be determined, for a given drawing-oft speed vain/min a given spinning bath temperature T C. and a given titer r of an individual filament in denier, according to the empirical formula In is a factor varying with the temperature; its values for various temperatures are given in the following table:

At the distance a from the spinning nozzle determined by the formula noted above, the filament mass has the requisite viscosity.

Inasmuch as the tensile stress involved in the second condition noted above, for all practical purposes can be produced only by a system of deflecting rodsWhich system, however, must be disposed in a comparatively large vessel wherein the spinning bath can have only a very low velocity-the necessary low relative velocity between filament and spinning bath can be obtained only by the use of a low spinning velocity. The value of the spinning velocity is determined by the requirement that the stress on the capillary filament due to friction must not exceed 50 dyu./cm. since with greater stresses, the surface of the filament is injured perceptibly.

The third condition noted above calls for a slow stretching procedure which is taken care of, chiefly, by keeping the drawing-off speed low, for radiographic investigations have demonstrated that the orientation of the lamellar micelles is the more enhanced, in the plane of the lamellae as well as in the direction of the axis of the micelles, the more slowly stretching takes place. Besides, this mechanism is increasingly facilitated the higher is the degree of stretching, i. e. the ratio of the filament sections before and after stretching, respectively.

These procedures can be expressed by the equation wherein Z represents the time in seconds which it takes a filament particle to travel the distance from the optimum state to the blue filament state, and St represents the degree of stretching.

Thus, the greater is this distance, i.e. the more slowly coagulation proceeds, the lower, therefore, is the temperature of the precipitating Water which determines the speed of coagulation, and the lower is the drawing-off speed, the better is the orientation, for a given degree of stretching.

Tests have demonstrated that a time Z of 0.6 second, and a degree of stretching St of 2, and therefore is to be considered about the minimum value required for insuring a degree of orientation which yields strengths materially exceeding those normally obtainable.

This condition is met by a spinning device and spinning method exemplified in the following example, and illustrated in the attached drawing which illustrates diagrammatically the conditions described in the example.

In the drawing, the sole figure thereof shows in diagrammatic section, the arrangement of a funnel and the vessel and deflecting rods associated therewith for purposes of the invention, as explained below.

The capillary filaments emerge, in form of a solution, from the apertures of a shower type spinning nozzle 1 to enter a funnel 2 which for purposes of a preliminary test, was made 10 cm. long and which was supplied with precipitating liquid (water) of 15 C., at the rate of 3 to 5 cc. per second.

At a spinning velocity of about 10 m./min. the filaments draw themselves out, until they reach the end of the funnel, to about twice their ultimate section (a phenomenon almost exclusively due to their overweight with respect to the spinning water), to arrive, at the end of the 3 funnel, at the optimum state. According to the formula given above, the distance of the optimum state from the spinning nozzle is Since, however, in this case the filaments in the funnel are drawn out somewhat less than in a normal spinning procedure, the value for a obtained above must be increased by an amount appraised at about 30 percent. This means that the funnel must have a length of 12 cm. At the end of the funnel the filaments have a velocity which equals half the drawing-oft velocity, i. e., 5 m./min.

The bottom opening of the funnel 2 dips into the surface the location of which is fixed by an overflow arrangement, of a precipitating bath contained in the vessel 3 and supplied to this vessel through an inlet 4 at a temperature such that after mixture with the cooler water flowing from the spinning nozzle 1, the water in the vessel 3 is maintained at a temperature of about 21 to 22 C. For this temperature, a drawing-off velocity of 10 m./min. and a medium filament velocity of 7.5 m./min. or 1.3 cm./sec., the distance traveled by the filament mass to coagulate from the optimum state to the blue filament state, is 8 cm. and the time it takes the filament to traverse this distance, is 0.6 sec.

The stretching proper is effected by means of the defleeting rods 5 which are displaced with respect to one another so that the angles formed by the filaments about the rods become increasingly smaller as the filament proceeds from the top of the vessel 3 toward the bottom thereof whereby, because of the progress of coagulation, the forces also increase steadily.

The precise positioning of the deflecting rods 5 must be ascertained on an empirical basis.

On leaving the last deflecting rod (the lowermost in the drawing), the bundle of filaments enters the discharge pipe of the vessel 3 wherein the final coagulation of the filaments is completed. The discharge section of this pipe must be provided very narrow (about 3 to 4 mm.) so that the volume of water discharged is limited in spite of its exposure to free pressure.

On emerging from the discharge pipe the filament, as usual, is deflected by a rod to continue its travel horizontally whereupon it is acidified and passed on to the winding device.

Given an arrangement and spinning conditions as exemplified in the above example and illustrated in the attached drawing, filaments having a tensile strength of from about 400 to about 500 g./100 den. can be spun.

While I have disclosed an embodiment of the invention and a mode of carrying it into eifect, it will be readily apparent. tothose skilled in the art that the invention as illustrated in the foregoing specification and in the attached drawing, is susceptible to numerous variations without departure from the spirit of the invention or sacrifice of the advantages thereof. Accordingly, the scope of the invention is to be understood as limited solely by the appended claims.

I claim:

1. The method of producing filaments of .high tensile strength from cuprammonium cellulose solutions which comprises passing the filaments into a funnel shaped bath, allowing the filaments. to partially coagulate in said bath so that at the end of the bath the filaments have an opti mum viscosity of 50,000 to 60,000 poises, passing the filaments into a second bath, subjecting the filaments to the action of braking means for the filaments so as to increase the length of travel and uniformly apply stretching tension, and drawing oil the filaments at the end of the second bath at more than twice the speed of the filaments at optimum viscosity whereby the filaments have been stretched to less than half their section at the point of optimum viscosity, the length of filament path in said second bath and the drawing oft velocity being such that the time of filament passage from the point of optimum viscosity through the second bath is at least 0.6 second.

2. Spinning apparatus for producing high strength silk from a cuprammonium cellulose solution, comprising a shower type spinning nozzle, a funnel extending downwardly from said nozzle, a vessel receiving the lower end of said funnel and extending downwardly therefrom, means in the bottom of said vessel for supplying a liquid thereto, means near the top of said vessel to provide an overflow for said liquid whereby to control the surface of said liquidin relation to the end of said funnel, a discharge pipe in the bottom of said vessel having a narrow aperture, and a series of deflecting rods so arranged in said vessel that the included angles about said rods formed by a filament. passing across said rods, decrease steadily in downward direction.

References Cited in the file of this patent UNITED STATES PATENTS 1,494,841 Holken May 20, 1924 1,646,788 Elsaesser et al Oct. 25, 1927 1,828,497 Hartmann Oct. 20, 1931 2,288,982 Watermann July 7, 1942 2,348,415 Polak May 9, 1944 FOREIGN PATENTS 347,878 Great-Britain May 7, 1931 738,054 France Dec. 20, 1932 

1. THE METHOD OF PRODUCING FILAMENTS OF HIGH TENSILE STRENGTH FROM CUPRAMMONIUM CELLULOSE SOLUTIONS WHICH COMPRISES PASSING THE FILAMENTS INTO A FUNNEL SHAPED BATH, ALLOWING THE FILAMENTS TO PARTIALLY COAGULATE IN SAID BATH SO THAT AT THE END OF THE BATH THE FILAMENTS HAVE AN OPTIMUM VISCOSITY OF 50,000 TO 60,000 POISES, PASSING THE FILAMENTS INTO A SECOND BATH, SUBJECTING THE FILAMENTS TO THE ACTION OF BRAKING MEANS FOR THE FILAMENTS SO AS TO INCREASE THE LENGTH OF TRAVEL AND UNIFORMLY APPLY STRETCHING TENSION, AND DRAWING OFF THE FILAMENTS AT THE END OF THE SECOND BATH AT MORE THAN TWICE THE SPEED OF THE FILAMENTS AT OPTIMUM VISCOSITY WHEREBY THE FILAMENTS HAVE BEEN STRETCHED TO LESS THAN HALF THEIR SECTION AT THE POINT OF OPTIMUM VISCOSITY, THE LENGTH OF FILAMENT PATH IN SAID SECOND BATH AND THE DRAWING OFF VELOCITY BEING SUCH THAT THE TIME OF FILAMENT PASSAGE FROM THE POINT OF OPTIMUM VISCOSITY THROUGH THE SECOND BATH IS AT LEAST 0.6 SECOND. 